This invention relates to a method and a system for blow molding a superplastic metal plate by applying to it a pattern of pneumatic pressure (a curve of the pneumatic pressure in relation to time) that is based on the maximum value of the strain rate of the superplastic plate as a set pattern of pneumatic pressure in relation to time when the superplastic plate is subjected to a high-speed blow molding.
Recently a method has been developed for blow molding a superplastic plate such as an aluminum plate after it has been heated to a desired temperature. Since in this method the shape and the thickness of the plate vary as its formation proceeds, maintaining proper superplastic conditions relating to the strain rate is difficult, and there is a difficulty in achieving a stable formation. Thus, a system for controlling the pneumatic pressure of the blow molding such that the maximum strain rate of the plate is kept constant during its formation has been discussed. In an example of this conventional control system, the maximum value of the strain rate is kept at a desired value (see Plasticity and Work [Journal of the Society of Japan Plastic Work] 31, 1990, p.1128, by Akio Takahashi, et al., and Materials Science Forum, Vols. 304-306, 1990, p.777, by N. Suzuki et al.). Since in this control system the strain rate of superplastic material is in an order of 10xe2x88x923 [1/s] and the obtained pattern of pneumatic pressure varies gradually, the strain rate can be easily controlled.
However, recently a high-speed blow molding has been developed, wherein the strain rate of superplastic material is equal to or more than 10xe2x88x922 [1/s], which is faster by one order than the conventional strain rate, resulting in less time being required for blow molding it. Since in such a high-speed blow molding the optimal pattern of the pneumatic pressure to keep the maximum value of the strain rate at a desired value varies greatly, it became difficult to control the pattern of the pneumatic pressure as desired by a conventional blow molding machine.
The present invention has been conceived in view of such circumstances. The purpose of it is to provide a method and a system that can appropriately perform blow molding even if the strain rate of a superplastic material is more than 10xe2x88x922 [1/s], wherein a pattern of pneumatic pressure based on the maximum value of the strain rate is applied to the material as a set pattern of the pneumatic pressure.
To the above end, in one aspect the method of the present invention of blow molding superplastic material is a method for blow molding a superplastic metal plate wherein pneumatic pressure in relation to time and based on a maximum value of a strain rate of the superplastic metal plate is applied to the metal plate as a set pattern of pneumatic pressure in relation to time when the metal plate is subjected to a high-speed blow molding after being heated to a desired temperature, comprising the steps of: entering data on a shape into which the metal sheet is to be blow molded and on the properties of a material of the metal plate to store the data in a storage; determining a set pattern of pneumatic pressure in relation to time from the entered data on the shape and the properties of the metal sheet; dividing the set pattern of the pneumatic pressure into an appropriate number of parts in relation to time; determining values of parameters for controlling the pneumatic pressure for each part divided from the set pattern of the pneumatic pressure; and controlling the pattern of the pneumatic pressure using the determined values of the parameters for controlling the pneumatic pressure.